Nanoscale Metallic Iron for Environmental Remediation: Prospects and Limitations

The amendment of the subsurface with nanoscale metallic iron particles (nano-Fe(0)) has been discussed in the literature as an efficient in situ technology for groundwater remediation. However, the introduction of this technology was controversial and its efficiency has never been univocally established. This unsatisfying situation has motivated this communication whose objective was a comprehensive discussion of the intrinsic reactivity of nano-Fe(0) based on the contemporary knowledge on the mechanism of contaminant removal by Fe(0) and a mathematical model. It is showed that due to limitations of the mass transfer of nano-Fe(0) to contaminants, available concepts cannot explain the success of nano-Fe(0) injection for in situ groundwater remediation. It is recommended to test the possibility of introducing nano-Fe(0) to initiate the formation of roll-fronts which propagation would induce the reductive transformation of both dissolved and adsorbed contaminants. Within a roll-front, Fe(II) from nano-Fe(0) is the reducing agent for contaminants. Fe(II) is recycled by biotic or abiotic Fe(III) reduction. While the roll-front concept could explain the success of already implemented reaction zones, more research is needed for a science-based recommendation of nano-Fe(0) for subsurface treatment by roll-fronts.